The present invention generally relates to shock absorber mechanisms for rotary applications and more particularly to shock absorber mechanisms suitable for rotary actuators.
Quickly stopping the rotation in a rotating machine can create large impact loads which can cause part distortion and stress failures. Repetitive smaller impact loads can also cause similar problems. Stress failures can lead to a break down in the rotating machine. Part distortion can lead to inaccurate control and inefficiencies.
One such rotating machine where this is a problem is in variable position rotary actuators. Variable position rotary actuators typically rotate a shaft between two angular positions (and discrete angular positions therebetween in some actuators) for a wide variety of purposes such as controlling the degree of opening of a butterfly valve for example. In such applications, it is often desired to have quick acceleration and high velocity such that the actuator can respond quickly to demands. To properly stop the shaft at the ends of the oscillating movement, mechanical stops are often used to stop the rotation. Such speed requirements and stopping requirements are not easily reconciled and cause significant impact loads. Overtime, these impact loads can cause stress failures or part distortion both of which are undesirable.
In view of the foregoing, it is an object of the present invention to provide a practical way to reduce impact in rotating machines.
It is a further object in this regard to improve the accuracy of such rotating machines, particularly over time.
It is an object of the present invention according to one important aspect to provide for impact reduction in rotary actuators that rotate a shaft between two angular positions and various discrete positions therebetween if desired.
In accordance with these and other objectives, the present invention comprises a shock absorber mechanism for a shaft having an axis of rotation. A shoulder is provided on the shaft for support of the shock absorber. The shock absorber further comprises a collar having an opening receiving the shaft. A clearance gap is defined between the collar opening and the shaft. A pin offset from the axis connects the collar to the shoulder. At least one resilient member arranged in the gap engages the collar and the shaft. In operation, the collar and the shaft rotate in unison. However, when one of the collar and the shaft accelerates relative to the other (such as to come to a sudden stop), the resilient member compresses to thereby to provide the shock absorption.
It is an aspect of the present invention that the shock absorber mechanism is incorporated into a rotary actuator. The shaft carries the actuator output. The collar includes a stop tab that has an oscillating travel path between two stop surfaces of the actuator housing. When the stop tab strikes one of the stop surfaces, the resilient member compresses thereby absorbing and reducing impact force.
Other objectives and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.